Electron discharge device subject to hydrocarbon background pressure and having carbon-dissolving electrodes



lfi- 1970 P. P. COPPOLA ETAL 3,526,799

ELECTRON DISCHARGE DEVICE SUBJECT TO HYDROCARBON BACKGROUND PRESSURE AND HAVING CARBON-DISSOLVING ELECTRODES Filed May 26, 1967 [r7 ven 23 ans.- Pafiiv c/r P Cappo/a, H0 er H Glance/(3J1? b i M! i. W The/r Aziorney United States Patent US. Cl. 31382 5 Claims ABSTRACT OF THE DISCLOSURE An electron discharge device to be operated in an evacuated system having low background pressure of hydrocarbon includes an electron gun for generating an electron beam and an anode having a narrow aperture through which a portion of the beam passes. To eliminate undesired deposition of carbon on the surface of the anode and in the aperture, which deposition tends to obstruct the passage of electrons, the anode is formed of a material capable of dissolving and diffusing carbon into the interior of the anode, vanadium being a preferred material, and is supported by a low thermal conductivity support so that the anode is heated by the electron beam to a temperature below the melting point of the material but sufficiently high that carbon deposited on the anode and in the aperture is dissolved into the anode and removed from its surface and the aperture.

This invention relates to electron discharge devices and electrodes therefor and particularly to electron discharge device electrodes capable of maintaining their intended electrical properties in the presence of a hydrocarbon atmosphere. This application is a continuationin-part of our application Ser. No. 421,020 filed Dec. 24, 1964, now abandoned, and assigned to assignee of this application.

In patent No. Re. 25,169, issued to William E. Glenn, Jr., on May 15, 1962, there is described and claimed a system for recording on a deformable medium. According to the patented system an electrical input signal applied via an electron beam acts to establish deformation patterns in such deformable medium. These patterns are capable of deflecting or modulating light applied to the medium and are generally in the nature of diffraction phase gratings having a first parameter corresponding to a given color component of an input signal and a second parameter corresponding to the intensity of such component. When properly illuminated in a projection system the diffraction grating diffracts light around a set of bars to produce an image, for example, a pictorial image corresponding to the recorded information.

A deformable medium useful in this recording system takes the form of a hydrocarbon recording oil which has the property of emitting a carbonaceous vapor as it is bombarded with an electron beam. The presence of this vapor causes a deposit upon component parts of the recording system and in particular upon the electrode elements of the electron gun altering the electrical properties and the efficiency of the electron emitting structure. For instance, the aperture of the electron gun anode through which a portion of the electron beam passes appears to reduce in size rendering the discharge device very inefficient after an extended period of operation and even resulting in complete closing of the aperture. This aperture blockage has presented a difiicult problem.

It is therefore an object of the present invention to provide an electron discharge device including electrodes 3,526,799 Patented Sept. 1, 1970 capable of maintaining their electrical characteristics in a carbonaceous atmosphere. It is another object of the present invention to provide an apertured electron discharge device electrode capable of maintaining such aperture in operative condition despite the presence of a carbonaceous atmosphere.

In accordance with the present invention, an electron discharge device cooperating with material producing a carbonaceous environment includes an anode electrode or the like which is pervious to the element carbon. In particular, an apertured anode electrode is formed of material having high carbon solubility and a high diffusion coefiicient for carbon when elevated in temperature. We have discovered that carbonaceous vapor present in the discharge device becomes dissociated at the anode electrode leaving elemental carbon heretofore responsible for blockage of the aperture. However, an electrode formed of the carbon sorbent material operating at the proper temperature dissolves the carbon and the carbon diffuses into the interior of the electrode leaving the outside surface including the aperture free of carbon deposit. The electrode is preferably heated through the medium of electron bombardment and is of such size that the electron bombardment raises the electrode temperature for attaining a high degree of carbon diffusion and solubility. In particular, the electrode is formed of vanadium, thorium, niobium, rhenium, or tantalum, and is operated at a temperature on the order of 1000" C. or higher.

The subject matter which we regard as our invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements.

In the drawings,

FIG. 1 illustrates a cross-section of a portion of an electron discharge device in accordance with the present invention, and

FIG. 2 is a view of an electron discharge device for a light valve projection apparatus illustrating an em bodiment of the present invention.

In this device, an electron beam 1 is emitted from a heated cathode 2 and passes through a grid structure 3 where it is directed by the electric field present between grid structure 3 and cylindrical anode 4 to follow a path through an axial aperture 5 in anode 4. The aperture 5 in anode 4 is quite small, typically on the order of 0.0008 inch in diameter for a depth of about 0.005 inch, for the purpose of producing a small electron beam 1 suitable for recording upon a writing medium (not shown) which may comprise an oil or a carbonaceous or hydrocarbon material. Some materials of this type are set forth in Pat. 2,943,147 issued to William E. Glenn, Ir., on June .28, 1960. Aperture 5 separates the electron discharge device into two chambers, chamber 6 including the electron beam generating apparatus and a chamber 7 which may include such carbonaceous medium. Passage of carbonaceous vapors between the chambers is desirably hindered on account of the deleterious effects such vapors have upon the electron gun cathode. The aperture 5 is made small for this additional reason.

We have discovered the narrowing and plugging of aperture 5 occurring heretofore resulted from the deposition of carbon. The carbonaceous vapor tends to dissociate upon the anode surface leaving carbon which changes the electrical characteristics of the anode and tends to close off or restrict the aperture 5. Thus we have found that many conventional anode materials such as copper, brass, chromium, molybdenum, tungsten, and titanium, are not suitable for operating in such environment. After a very short period of time the aperture in such material becomes plugged with carbon and the system ceases to operate because most of these materials do not have a high solubility for carbon at the operating temperature, or have too low a diffusion coefficient for carbon at such temperature. Again, we have found that titanium, for example, cannot be operated at the high temperature required for dissolving carbon. Further, titanium, cobalt. and iron have a high vapor pressure and low melting point, which makes these materials undesirable. On the other hand, molybdenum and tungsten possess unsatisfactory solubility and diffusion coefficients for carbon. While nickel gives a marginal performance, the material to be used should have the following characteristics at the high operating temperatures required, namely, a low vapor pressure, a high diffusion coefficient for carbon, and a high solubility for carbon.

To solve the above mentioned problem, therefore, in accordance with the present invention, anode 4 is formed of a material having the properties of good carbon solubility and diffusion. The dissociated carbon, around aperture 5, is absorbed into anode 4 where it diffuses into the bulk of the anode material. A considerable quantity of carbon can be removed in this way whereby the lifetime of the electron discharge device is greatly increased. Preferred materials for anode 4 are vanadium and thorium, At a desirable operating temperature of 1000 C., these materials have the following properties;

While nickel would appear to have satisfactory performance according to these values, it is not a preferred material at temperatures above 700 C. since it has a low melting point and high vapor pressure. Thus, while it does perform satisfactorily in monochrome recording systems, it is not recommended for use in color recording systems.

Vanadium has a high diffusion coefficient and also offers the highest melting temperature (1900 C.) and therefore the maximum protection in the case of temporary overheating. In the illustrated embodiment the cylindrical anode has an outside diameter of 0.250 inch and an axial thickness of 0.150 inch resulting in a volume of approximately 0.08 cm. and can therefore contain up to about grams of carbon before saturation occurs. For carbon a deposition rate at aperture 5 of 10- grams/cnm hr., which is representative, the large diffusion coefiicient of vanadium permits remote regions of the anode operating at 1000 C. to reach over 90 percent saturation before the aperture region becomes saturated. For the embodiment illustrated wherein the aperture 5 is 0.0008 inch in diameter by approximately 0.005 inch in length extending from the end of the anode, the surface area of the aperture is approximately 8X10" cm. so the rate of carbon deposition in the aperture is approximately grams/hr. This provides an operating time of over 10 hours before the aperture region of the anode becomes saturated.

In the illustrated device, about 4 watts were available for heating the anode from the electron beam. In order to reduce thermal losses, the anode is supported around its periphery with a cylinder 8 of refractory material, e.g., hafnium, with about a 0.001 inch wall thickness. Cylinder 8 is in turn secured to wall 12 separating chambers 6 and 7. A radiation shield cylinder 9 surrounds cylinder 8 and anode 4. Anode 4 is also desirably provided with an axial also suitable. Thorium is of particular interest because of its high solubility for carbon. An anode including either i of the metals vanadium or thorium operates within the temperature range of from about 700 C. to about 1400 C., With 1000 C. being given as a typically desirable.

operating temperature. The size of the anode is selected so the heating power available from electron bombardment or heat otherwise provided is sufficient to raise the anode to the desired temperature range. If a lesser amount of heating power is available, for instance from a smaller electron beam current, the anode may be accordingly reduced in size. Thus, by way of example, if only one watt of heating energy is available from the electron beam, the anode volume and support diameter are conveniently reduced so that radiation and conduction losses for instance at an operating temperature of 1000 C., total one watt. Size reduction can be considerable without impairing the tremendous carbon absorption capability of the electrode.

Certain other carbon absorbing materials are also useful in the formation of electrodes in accordance with the present invention, for example, niobium, rhenium, and tantalum. An anode formed of the latter materials should be run at a-ternperature 400 to 500 C. higher than an electrode formed of the first two materials mentioned for comparable carbon absorption rates on account of the lower diffusion rate and carbon solubility of niobium, rhenium, and tantalum. These materials can of course be raised to much higher temperatures because of their higher melting points.

In FIG. 2 the electron discharge device illustrated in FIG. 1 is shown as used in the type of light valve projection apparatus disclosed in US. Pat. 3,289,028 Shilling et al., granted Nov. 29, 1966. The apparatus 13 comprises an envelope member which forms a writing chamber and which is identified generally as 14 and an appendage elec I tron discharge device of a type illustrated in FIG.-1 and identified generally as 15. Although various other envelope configurations may be provided, the envelope member 14 may conveniently be fabricated of glass to the generally boot-shaped configuration illustrated. The writing. chamber includes a reservoir and a target region 16 for storing a writing medium, a deflection region 18 wherein means (not shown) are provided for deflecting an electron beam and a neck region 20 for supporting the device 15. A disk 22 of transparent material such as glass and having a conducting substrate surface 23 positioned thereon is mounted by means (not shown) in the reservoir and target region 16 of the writing chamber. This is mounted in a manner which provides that an outer segment of its surface area is partially immersed in a pool 24 of a writing medium, such as a suitable oil containing a hydrocarbon. The disk is rotated by means (not shown) and a layer 26. of the writing medium forms on the surface of the disk. Through this arrangement the writing medium is both supported in a raster area, indicated by the jagged surface 28, and continuously replenished.

An electron beam is generated by the electron gun appendage member 15 and is accelerated toward the raster target area 28 by high potential applied between the cathode of the electron gun and a conductive substrate 23. In order to simplify the drawings, the means for providing this high potential is not illustrated.

It is thus apparent that the present invention provides an electron discharge device and electrode therefor capable of sustained operation in an environment including hydrocarbon constituent material. Deposits of carbonaceous vapor upon electrode surfaces are absorbed in the form of carbon into the electrode. The electrode and aperture surfaces thereby retain their original contour over an extended apparatus lifetime.

While we have shown and described several embodiments of our inventionQjit will be apparent to those skilled in the art that many changes and modifications may be made without departing'from our invention in its broader aspects; and we therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electron discharge device comprising: a first chamber for accommodating a deformable recording medium including hydrocarbon constituents; a second chamber including an electron beam emitting member; a wall separating said chambers and containing a relatively large aperture therein; an anode electrode provided with a beam limiting aperture through which a portion of the electron beam passes, 'said anode electrode including a carbon dissolving material selected from the group consisting of thorium, vanadium, niobium, rhenium, tantalum and nickel and having an axial central opening larger in diameter than said beam limiting aperture extending from one of said chambers to said beam limiting aperture; a thin cylinder formed of low thermal conductivity material secured to said wall and supporting said anode electrode for the minimum conduction of heat therefrom whereby said electron beam raises said electrode temperature to between 700 C. and 1400 C., said cylinder and anode cooperating with said wall in separating said chambers; and a thermal radiation shield secured to said wall surrounding said cylinder and said anode to facilitate heating of said anode and dissolution of carbon deposited thereon.

2. The electron discharge device of claim 1 in which said anode electrode consists essentially of vanadium.

3. The electron discharge device of claim 1 in which said anode electrode consists essentially of thorium.

4. The electron discharge device of claim 1 in which said anode electrode consists essentially of tantalum.

5. The electron discharge device of claim 1 in which said thin cylinder comprises hafnium.

References Cited UNITED STATES PATENTS 1,684,263 9/1928 Coolidge 313 2,329,320 9/ 1943 Atlee 313-55 3,253,086 5/1966 Campbell 1787.87 2,418,390 4/1947 Atlee 313-178 2,453,118 11 /1948 Buckingham et al. 313--218 X 2,644,906 7/ 1953 Bondley 313348 X 2,828,433 3/1958 Frenkel 31382 3,289,028 11/1966 Schilling et al. 31382 X 3,331,981 7/1967 Lafferty 313-178 ROBERT SEGAL, Primary Examiner US. Cl. X.R. 

